| Study of the mitochondrial ABC transporter protein ABCB6 |
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ABCB6 belongs to the B [MDR/TAP] sub-family of ATP-binding cassette
transporters. The B subfamily consists of 11 members, with functions
ranging from peptide transport (ABCB2-3) to secretion of bile acids
(ABCB11). ABCB1-MDR1, the first human ABC transporter cloned and
characterized through its ability to confer an MDR phenotype to cancer
cells, stands out among ABC transporters by conferring the highest
resistance against the greatest variety of compounds.
In addition to the four full-length transporters, the ABCB subfamily contains seven half transporters, of which four (ABCB6, ABCB7, ABCB8 and ABCB10) are believed to reside in the mitochondria. The function of the human mitochondrial ABC proteins is unknown. The outer membrane of mammalian mitochondria is freely permeable to most small molecules, whereas the inner membrane forms an impermeable barrier between the mitochondrial matrix and the cytosol. Based on the general role of ABC transporters, members expressed in the mitochondria are likely to play a role in transport processes through the inner membrane (thus regulating the intramitochondrial milieu), or in the communication of signals transmitted from the mitochondria to the rest of the cell. Although sequence conservation alone does not allow the exact determination of function, possible roles of mitochondrial ABC transporters include the export of toxic substances that accumulate in the mitochondrial matrix (cf. ABCB1), export of peptides (cf. ABCB2-3) or transport of phospholipids (cf. ABCB4). Furthermore, depending on their orientation in the membrane, ABC transporters may also be involved in the import of certain constituents.[1]
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